Engine sputters out when brakes are applied

I have a 69 Dart, 340, 4-speed with manual drum brakes.

Background Info: Car sat for 10 yrs and now I’ve got it going again. Completely new drums and all internal parts. New brake lines and distribution block. I did not install a new master cylinder. Replaced gas tank and fuel lines. New fuel pump. Rebuilt carb. Car ran awesome for 2 months.

BUT now when I press the brakes enough to get stopped the engine sputters out and dies. It’s manual brakes so no vacuum. I am no master mechanic and need some suggestions on what to do.

Thanks